A conventional commercial aircraft generally includes a fuselage, a pair of wings, and a propulsion system that provides thrust. The propulsion system typically includes at least two aircraft engines, such as turbofan jet engines. Each turbofan jet engine is mounted to a respective one of the wings of the aircraft, such as in a suspended position beneath the wing, separated from the wing and fuselage. Such a configuration allows for the turbofan jet engines to interact with separate, freestream airflows that are not impacted by the wings and/or fuselage. This configuration can reduce an amount of turbulence within the air entering an inlet of each respective turbofan jet engine, which has a positive effect on a net propulsive thrust of the aircraft.
However, a drag on the aircraft, including the turbofan jet engines, also has an effect on the net propulsive thrust of the aircraft. A total amount of drag on the aircraft, including skin friction and form drag, is generally proportional to a difference between a freestream velocity of air approaching the aircraft and an average velocity of a wake downstream from the aircraft that is produced due to the drag on the aircraft.
Positioning a fan at an aft end of the fuselage of the aircraft may assist with reducing an overall drag on the aircraft by reenergizing a boundary layer airflow over the aft end of the fuselage. The inventors of the present disclosure have discovered that increasing an amount of relatively low momentum boundary layer air ingested by the fan at the aft end can increase an efficiency of the aft fan. Accordingly, an aft fan configured to maximize an amount of relatively low momentum boundary layer air ingested would be useful.